Hydraulic priority valve

ABSTRACT

A hydraulic priority switch for preferential feeding of a low consumption primary loop in fluid communication with a hydraulic reservoir which is chargeable from a pressure medium source via a flow control means, against a non-preferential secondary loop which can be switched in with the aid of a priority value when said primary loop is sufficiently pressurized, said hydraulic priority switch having protecting means for protecting both loops from excess pressure comprising a pressure-limiting valve which functions to make an outlet flow path available when pressure is excessive.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to hydraulic priority valves for preferentialdirection of fluid pressure, particularly for hydraulic devices onvehicles.

2. Description of the Prior Art

It is known to install priority valves when, on reasons of operatingsafety or reliability or in order to achieve a specific schedule offunctions, one of two or more consuming devices must be suppled withpressure medium before an additional consuming device is connected tothe source of that pressure medium. An example from the standpoint ofoperating safety or reliability might be a vehicle wherein a power brakeand a level control are fed from a single pump. Clearly the brake, whichis critically important to safety, must be given priority. An examplefrom the standpoint of a schedule of functions might be the operatingsequence (a) hydraulic gripping of a workpiece and (b) advance of atool. Here clearly, the advance should only occur following thegripping.

A known priority valve (German laid-open application No. 23 56 235)employs a bypass valve which is hydraulically servo-controlled. Thepressure medium flows from the pressure medium source through a checkvalve to a hydraulic accumulator and to the preferred consuming device.The pressure in the hydraulic accumulator serves as the control pressurefor a preliminary control piston and an active surface of a main controlpiston, with the second active surface of said main control piston beingrelieved from or supplied with the control pressure depending on thestate of charging of the hydraulic accumulator. The main control pistonconveys the pressure medium stream to the non-preferred consuming devicewhen the hydraulic reservoir is adequately charged.

The pressure-limiting valve may, at various times, be exposed to thepressure of the hydraulic accumulator. Such an arrangement is indeedfunctionally very reliable and is adequate for many applications. If,however, the preferred consuming device is required always to operatewith the same pressure to the extent possible, as is desired for examplein the case of a power brake with an accumulator, this cannot be broughtabout by a bypass valve. This stems from the fact that bypass valvesordinarily have switching-pressure differentials.

Accordingly the underlying problem of the invention is to devise ahydraulic priority valve of a suitable type wherein the consuming devicewhich is preferentially supplied, and is in particular discontinuouslyoperated, has the same pressure level available at all times. Thispressure level should be, in particular, independent of any consumptionon the part of other consuming devices. Said valve should be simple andinexpensive, with a minimum of parts, and in particular, should besuited to mass production. The installation space required should besmall enough so that the entire assembly can be constructed as anattachment to a hydraulic accumulator.

SUMMARY OF THE INVENTION

This invention provides a hydraulic priority valve for preferentialfeeding of a low consumption primary loop in fluid communication with ahydraulic accumulator which is chargeable from a pressure medium sourcevia a flow control means (such as a check valve), against anon-preferential secondary loop which can be switched in with the aid ofa priority valve when said primary loop is sufficiently pressurized;said hydraulic priority valve having protecting means for protection ofboth loops from excess pressurization, the protecting means preferablycomprising a pressure-limiting valve which functions to make an outletflow path available when pressurization is excessive.

In particular, this invention provides an improvement in the abovehydraulic priority valve wherein: the priority valve is a sequence valvein a structural module with the pressure-limiting valve, having amoveable valve element means (preferably a slideable control piston)with a hydraulic fluid interface surface (preferably the control pistonend face and blind hole), which valve element acts against the force ofa resistance means (preferably a return spring), said valve elementbeing permanently pressurized from the pressure medium source(preferably hydraulic fluid); whereby, when a first given pressure isattained a first pressure medium flow path is opened from a pressureconnection which is upstream of the flow control means (preferably acheck valve) to a first consuming device connection which is linked tothe secondary loop, said first pressure medium flow path being activatedby the movement of the valve element (preferably the sliding of thecontrol piston); and whereby when a second, higher given pressure isattained a second pressure medium flow path is opened to direct thepressure medium to an outlet connection (such as a nipple) and back tothe tank, said second pressure medium flow path being activated by afurther sliding of the valve element in the same direction.

With the above solution, the charging and relieving of the hydraulicaccumulaor which occurs with bypass valves is avoided. In the system ofthis invention, the hydraulic accumulator acquires the character andfunction of a safety reserve. Since the pressure medium source mustproduce a pressure at least as high as the first limiting pressure, aslong as there is no consumption in the primary loop, it is clear thatcirculation of the pressure medium in the unpressurized state is notpossible. However, this condition is not important if the flow of thefeed stream is small. Thus, it is quite normal with vehicular hydraulicdevices for pumps with feed stream flow rates of 1 dm³ /min (cubicdecimeters/ minute) or less to be used. The advantages achieved outweighthe small additional energy consumption.

Hydraulic sequence valves with turn-on valves or follower valves arethemselves known, but with these sequence valves, a specialpressure-limiting valve must be provided, as a result of which thenumber of necessary component parts in the system is practicallydoubled.

BRIEF DESCRIPTION OF THE DRAWING

The invention is illustrated in more detail with the aid of theembodiment shown in the drawing, wherein the embodiment is representedin part by means of hydraulic symbols.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A connecting piece 2 joined to a hydraulic accumulator 1 has sequentialadjoining coaxial first through fifth bore holes 3 through 7,respectively, of different diameters. The diameter of first hole 3 isgreater than that of second hole 4 which in turn is greater than that ofthird hole 5, and third hole 5 connects to fourth hole 6 and fifth hole7, of successively greater diameter. In second hole 4, a control piston8 is slidably mounted and is acted on by one end of a return spring 9located in first hole 3. The counter support for the other end of returnspring 9 is in a threaded cap 10 at one end of first hole 3 which isfurnished with a centrally disposed outlet nipple T in the form of atubing nozzle or the like. Control piston 8 has a central blind borehole 12 which begins at piston end face 11 lying opposite to returnspring 9 which connects at its end to the outer wall surface of controlpiston 8 via transverse holes 13. At a distance from the junction ofthird hole 5 and second hole 4, there is a ring-shaped groove 14 in andcoaxial with second hole 4; the edge of groove 14 which is closest tothird hole 5 is designated first control edge 15. A firstconsuming-device connection R is linked to groove 14. The shoulder edgeon second hole 4 at the junction of first hole 3 and second hole 4 isdesignated second control edge 16. Third hole 5 is linked to a pressureconnection P fed by a pressure medium source 17. The passage betweenthird hole 5 and fourth hole 6 serves as a seat 18 for a check valve 19which is acted on by a spring 20, which is guided in a cage 21 in theform of a sheet metal shaped piece. Fifth hole 7 has the shape of ashallow countersinking. Through junction opening 22, fifth hole 7 islinked to liquid space 23 of hydraulic accumulator 1 which has amembrane 25 which is furnished with a closing piece 24 and whichseparates liquid space 23 from a gas space 26. A conduit 27 leads fromhole 7 to a second consuming-device connection A, to which the primary(preferential) loop containing power brake device 28 is connected. Thepower brake has a closed center position whereby it consumes pressuremedium only when actuated and only in small amounts. A secondary(non-preferential) loop 33 is connected at first consuming deviceconnection R, which loop has a level-regulating valve 29 for regulatingthe height of an axle 32 which is sprung with the aid ofpiston-and-cylinder assembly 30 and hydraulic accumulator 31.

Level-regulating valve 29 has a center switching position forunpressurized circulation, which position corresponds to the heightdesired.

To illustrate the operation of the system, assume that the pressuremedium source 17 is delivering and that the hydraulic accumulator 1 isstill not sufficiently filled. The pressure medium then passes throughpressure connection P, third hole 5, check valve 19, fourth hole 6,fifth hole 7, and junction opening 22 into liquid space 23, which spaceconstantly enlarges as it is being filled. As long as there is noconsumption in the power brake, the pressure quickly attains a valuecorresponding to the potential or prestressing force of return spring 9.When the pressure increases further, the pressure force on piston endface 11 and the bottom of blind hole 12 exceeds the prestressing forceof return spring 9, and control piston 8 begins to move away from thepressure (downward in the FIGURE). When a given amount of pressure isattained, first control edge 15 is passed, and a passage is opened fromthe hydraulic fluid pressurized part of second bore hole 4 toring-shaped groove 14, and thus through first consuming-deviceconnection R to the secondary loop 33. The pressure at first controledge 15 does not increase further as long as no higher pressure isneeded in the secondary loop 33. If, however, a higher pressure isproduced in the secondary loop 33 due to overloading or closing ofoutlet passages or the like, the pressure increase is also transmittedto end face 11 and the bottom of blind hole 12 and it causes a further(downward) movement of control piston 8, which will continue until, at asecond given pressure, the transverse holes 13 move past second controledge 16. Beyond this point, there is a passage from second bore hole 4through blind bore hole 12, transverse holes 13, and first bore hole 3,to outlet nipple T, so that pressure medium source 17 is linked to theoutlet.

The design engineer has the freedom to make the difference between thefirst and second given pressures small. Since each pressure increasealso makes itself felt in the primary loop, the uniform pressureproperties which are desirable for the system will be better, thesmaller one makes the difference in given pressures. Since the firstgiven pressure is adequate for supplying the primary loop, a demandthere does not lead to emptying of the hydraulic reservoir but rather isimmediately met via the pressure medium source 17. It should be notedthat control piston 8 is not pressurized on its spring side. This meansthat the pressure drop at control edge 15 is proportionally greater theless the required pressure in the secondary loop. If, however, therequired pressure in the secondary loop is at the level of the firstgiven pressure, there is practically no pressure drop at control edge15, and the energy balance is very favorable. On the other hand, theenergy loss with small pumps is negligible in any event.

The invention is not limited to the embodiment represented. It is clearthat the configuration of the control piston is variable within widelimits, particularly with regard to its interaction with channels orholes in the housing. Thus, in general, holes and channels areinterchangeable and may be located at differing points. It is, ofcourse, important that the holes in the control piston not be located sothat all loops of fluid pressure medium are interconnectedsimultaneously, unless it is desired that the hydraulic priority valveoperates as a simple on-off valve. Thus, in the preferred embodimentillustrated in the drawing, transverse holes 13 cannot pass secondcontrol edge 16 until after end face 11 passes first control edge 15.The location and orientation of connections are also discretionary.Finally, the entire priority switch system may be accommodated in ahousing comprising a single structural module.

I claim:
 1. In a hydraulic priority valve for preferential feeding of alow consumption primary loop in fluid communication with a hydraulicaccumulator which is chargeable from a pressure medium source via a flowcontrol means, against a non-preferential secondary loop which can beswitched in with the aid of said priority valve when said primary loopis sufficiently pressurized, said hydraulic priority valve havingprotecting means for protecting both loops from excess pressurecomprising a pressure-limiting valve which functions to make an outletflow path available when pressure is excessive;the improvement whereinthe priority valve is a sequence valve in a structural module with thepressure-limiting valve, having a valve element means with a hydraulicfluid interface surface which valve element means acts against the forceof a resistance means, said valve element means being permanentlypressurized from the pressure medium source, whereby when a first givenpressure is attained a first pressure medium flow path is opened from apressure connection which is upstream of the flow control means to afirst consuming device connection which is linked to the secondary loop,said first pressure medium flow path being activated by the movement ofthe valve element means, whereby when a second higher given pressure isattained a second pressure medium flow path is opened by a valve memberacted upon by the pressure medium, to direct the pressure medium to anoutlet connection and back to the tank, said second pressure medium flowpath being activated by a further movement of the valve element means inthe same direction, and whereby after at least the first given pressureis attained, the valve element has been moved sufficiently to permit apermanent link between the pressure medium source and the firstconsuming device connection so that when the second given pressure isattained the secondary loop is linked to said outlet connection inaddition to being linked to the primary loop; and wherein the flowcontrol means is a check valve, the valve element means is a slideablecontrol piston having an end face opposite to the resistance means whichis a return spring, the hydraulic interface surface comprising at leastsaid end face in the control piston, and the pressure medium ishydraulic fluid; whereby when the first given pressure is attained, theend face passes a first control edge and as a result opens up a flowpath from a second bore hole which accommodates the control piston and athird bore hole which is connected to the pressure medium source, to aring-shaped groove located in the second bore hole which is linked to afirst consuming-device connection; whereby an inner blind hole extendinginwardly from the end face into the control piston is linked viatransverse hole means to the outer surface of the control piston at thebottom of the inner blind hole, so that when the second given pressureis attained, the transverse hole means moves into fluid communicationwith a first bore hole which is linked to the outlet connection.
 2. In ahydraulic priority valve for preferential feeding of a low consumptionprimary loop in fluid communication with a hydraulic accumulator whichis chargeable from a pressure medium source via a flow control means,against a non-preferential secondary loop which can be switched in withthe aid of said priority valve when said primary loop is sufficientlypressurized, said hydraulic priority valve having protecting means forprotecting both loops from excess pressure comprising apressure-limiting valve which functions to make an outlet flow pathavailable when pressure is excessive;the improvement wherein thepriority valve is a sequence valve in a structural module with thepressure-limiting valve, having a valve element means with a hydraulicfluid interface surface which valve element means acts against the forceof a resistance means, said valve element means being permanentlypressurized from the pressure medium source, whereby when a first givenpressure is attained a first pressure medium flow path is opened from apressure connection which is upstream of the flow control means to afirst consuming device connection which is linked to the secondary loop,said first pressure medium flow path being activated by the movement ofthe valve element means, and whereby when a second higher given pressureis attained a second pressure medium flow path is opened by a valvemember acted upon by the pressure medium, to direct the pressure mediumto an outlet connection and back to the tank, said second pressuremedium flow path being activated by a further movement of the valveelement means in the same direction; and wherein the flow control meansis a check valve, the valve element means is a slideable control pistonhaving an end face opposite to the resistance means which is a returnspring, the hydraulic interface surface comprising at least said endface in the control piston, and the pressure medium is hydraulic fluid;whereby when the first given pressure is attained, the end face passes afirst control edge and as a result opens up a flow path from a secondbore hole which accommodates the control piston and a third bore holewhich is connected to the pressure medium source, to a ring-shapedgroove located in the second bore hole which is linked to a firstconsuming-device connection; whereby an inner blind hole extendinginwardly from the end face into the control piston is linked viatransverse hole means to the outer surface of the control piston at thebottom of the inner blind hole, so that when the second given pressureis attained, the transverse hole means moves into fluid communicationwith a first bore hole which is linked to the outlet connection.
 3. Theimprovement of claim 1 or 2 wherein the bore holes are coaxial and arein numerical sequence; the first bore hole contains the return spring;the second bore hole contains the control piston, and has the ringgroove and first consuming device connection with first control edge;the third bore hole has the pressure connection; and the fourth borehole has the check valve at the junction point with the third bore hole.4. The improvement of claim 3 wherein the junction point between thefirst bore hole and the second bore hole forms the second control edge,so that when the control piston moves sufficiently, the transverse holemeans passes the second control edge and fluid flow is opened betweenthe first bore hole and the second bore hole.
 5. The improvement ofclaim 4 wherein one end of the return spring is seated in a cap on theend of the first bore hole opposite the junction with the second borehole, the other end engaging the control piston, said cap having theoutlet connection therein in the form of a nipple.
 6. The improvement ofclaim 5 wherein all of the bore holes are located in a single structuralmodule.
 7. The improvement of claim 6 wherein the primary loop containsa vehicular power brake device.